Method for operating cryocooler

Abstract

A method for operating a cryocooler, in which the cryocooler includes an expander including an expander motor that is connected to a power source by a power supply cable and is capable of being driven at a power source frequency, the method includes: releasing a connection between the power source and the expander motor by the power supply cable; connecting the power source and the expander motor via an inverter; executing an accelerated cooling operation of the cryocooler in which the power source frequency is converted into an operation frequency higher than the power source frequency by the inverter and the expander motor is driven at the converted operation frequency; and removing the inverter and reconnecting the power source and the expander motor, after the accelerated cooling operation is stopped.

What is claimed is: 
     
         1 . A method for operating a cryocooler, in which the cryocooler includes an expander including an expander motor that is connected to a power source by a power supply cable and is capable of being driven at a power source frequency, the method comprising:
 releasing a connection between the power source and the expander motor by the power supply cable;   connecting the power source and the expander motor via an inverter;   executing an accelerated cooling operation of the cryocooler in which the power source frequency is converted into an operation frequency higher than the power source frequency by the inverter and the expander motor is driven at the converted operation frequency; and   removing the inverter and reconnecting the power source and the expander motor, after the accelerated cooling operation is stopped.   
     
     
         2 . The method according to  claim 1 , wherein the cryocooler includes a first compressor for suctioning and discharging a working gas to and from the expander, and the first compressor is connected to the expander motor by the power supply cable as the power source. 
     
     
         3 . The method according to  claim 2 , wherein the connecting includes replacing the first compressor with a second compressor having a larger capacity than the first compressor,
 wherein the second compressor is connected to the expander motor via the inverter as the power source, and is used for the accelerated cooling operation.   
     
     
         4 . The method according to  claim 1 , further comprising:
 temporarily increasing an amount of a working gas of the cryocooler during the execution of the accelerated cooling operation.   
     
     
         5 . The method according to  claim 1 , wherein the cryocooler is used for cooling of a superconducting coil, and
 the superconducting coil is cooled by using an additional cooling device that supplies a cooled gas to a periphery of the superconducting coil, in addition to the accelerated cooling operation.   
     
     
         6 . The method according to  claim 1 , further comprising:
 before the releasing the connection between the power source and the expander motor by the power supply cable,
 executing a normal cooling operation of the cryocooler that drives the expander motor at the power source frequency; and 
 ending the normal cooling operation.